A primary function of a disk drive subsystem is to store data. Many host operating systems incorporate data access methods that require disk volumes to be initialized with a specific number of data records and a specific data content. The process of initializing a disk volume is called formatting and is generally performed by a format utility under control of a central processing unit.
Operating systems employ software utilities to format disk drive volumes, with many utilizing the count, key, data (CKD) format protocol. Such formatting actions can consume a substantial amount of time and processor resources. For example, although each formatted disk track contains the same information and predictable count fields, the format utility must write the CKD information on every track to be formatted. Such write actions require the use of the central processing unit resources, channel resources and disk subsystem resources. As the writing of data to a disk track is a slow process, such formatting is a substantial time-consuming function. For example, an IBM S/390 format utility can take as long as 20 minutes to format an IBM 3390 Model 3 Disk Volume.
The IBM RAMAC (IBM and RAMAC are trademarks of the International Business Machines Corporation) virtual array storage subsystem employs a virtual storage architecture in which functional volumes (i.e., virtual storage volumes) are represented as a set of pointers in tables. The IBM RAMAC system employs an operation called "SnapShot" wherein new views of a functional disk volume or data set are "snapped" by copying the pointers. None of the actual data is accessed, read, copied or moved.
To enable the operation of the SnapShot action, a log-structured file procedure is employed wherein updates to data are never done in place on the disk drives. More specifically, any updates that are made to the data are effective only for a particular view of the data and the other views remain unchanged. A log structured array functions as a true log file, in that only the last entry is valid. Thus, when a functional volume track is updated, the current updated copy is always written to the end of the log file, creating a gap in the disk system called "free space" which is recovered in a later action. Accordingly, when the RAMAC system updates a view of a functional volume, that update is written to a new location and the log of that view is then caused to reflect the new updated data location. The other views of the data remain the same and the pointers point to the pre-update version of the data.
Notwithstanding the speed of the data duplication action which results from a virtual array storage subsystem function, the formatting of a functional disk volume that is required by some host data access methods still requires the expenditure of large amounts of time and system resources.
Accordingly, it is an object of this invention to provide an improved method and apparatus for formatting a functional disk volume.
It is another object of this invention to provide an improved method and apparatus for formatting a functional disk volume which provides substantial speed advantages over prior art format utilities.